The use of hydrogen peroxide systems for disinfecting soft contact lenses is well known for its efficacy. Conventional disinfecting processes employing H.sub.2 O.sub.2 utilize either H.sub.2 O.sub.2 itself or a compound that yields H.sub.2 O.sub.2 such as a metal peroxide, percarbonate, alkylperoxide or the like. Most processes employ H.sub.2 O.sub.2 in a 3-5% by weight aqueous solution. Recently, Merianos et al. in U.S. Pat. No. 5,008,106, described a solid, anhydrous complex of PVP-H.sub.2 O.sub.2 that may be utilized to generate H.sub.2 O.sub.2 solution for disinfecting contact lenses.
Hydrogen peroxide disinfecting, however, requires that residual hydrogen peroxide remaining on the lenses after disinfecting must be neutralized or decomposed to a biologically inert state before the disinfected lenses may be placed on the eyes. Significant residual H.sub.2 O.sub.2 remaining on the lenses results in eye irritation, generally manifested by stinging sensations.
A number of neutralizing or reducing agents and methods are known in the art. Each neutralizing method is typically combined with a conventional aqueous solution source of H.sub.2 O.sub.2 for disinfecting the lenses. The prior art combinations with H.sub.2 O.sub.2 solution have certain disadvantages. For example, U.S. Pat. No. 3,912,451 teaches neutralizing residual hydrogen peroxide by contacting the H.sub.2 O.sub.2 disinfecting solution and lenses therein with a metal, such as platinum, that catalyzes decomposition. A difficulty arising from this system is that neither the H.sub.2 O.sub.2 solution, because of its strong oxidizing character, nor the solid form of the catalyst allow for the presence of a preservative. The resulting H.sub.2 O.sub.2 residual-free solution holding the lenses is not preserved. Thus, the solution and lenses are at risk of contamination and reinfection unless additional steps and solutions or compositions are added to the process.
Other agents are known in the art for decomposing hydrogen peroxide in contact lens disinfecting systems. Of particular interest, because it acts at a faster, more convenient rate, is the use of an enzyme, such as catalase. For example, U.S. Pat. Nos. 4,748,992 and 4,585,488 report effective decomposition of H.sub.2 O.sub.2 taking place within a few minutes of introduction of catalase. The process of patent '488 requires sterilizing a contact lens with an aqueous solution of H.sub.2 O.sub.2 and subsequently contacting the lens with an isotonic solution of dissolved catalase. Catalase in tablet form may be utilized but the H.sub.2 O.sub.2 source remains a conventional aqueous solution.
In addition to characteristics of the disinfecting/neutralizing chemicals per se, a major goal in designing lens care formulations relates to their methods of use. It is widely accepted that regimens for disinfecting and cleaning contact lenses must be as simple as possible to encourage lens wearers to comply with the care regimens as a matter of avoiding adverse health effects due to contaminated lenses. Any simplification in a regimen, such as by combining processing steps, combining chemicals, adding separate components at the same time, or the like is generally advantageous in seeking to achieve patient compliance.
Simplyifying lens care regimens by combining disinfecting and neutralizing components remains difficult to achieve because of the difficulty of balancing the relative reaction rates of the disinfecting and neutralizing processes. A difficulty with fast neutralizing of H.sub.2 O.sub.2 systems, such as catalase, is that the lenses to be effectively disinfected, must be exposed to a relatively high concentration of H.sub.2 O.sub.2 for a significant, finite period of time in order to achieve disinfecting before neutralizing proceeds significantly. The time required for disinfection is generally dependent upon the concentration of hydrogen peroxide utilized, requiring on the order of two hours at 1.0 weight percent H.sub.2 O.sub.2 while only five minutes at 3.0% by weight hydrogen peroxide. Since it is preferred that H.sub.2 O.sub.2 concentration be as low as possible, it is evident that if one desires, as a matter of simplifying a lens care regimen, to treat lenses simultaneously with hydrogen peroxide and a fast acting neutralizer, such as catalase, it is necessary to employ the neutralizer with care. In fact, it is preferable to delay the effective release of such a neutralizer in order to allow adequate time to achieve disinfecting and, thereafter, obtain substantially complete neutralization of the disinfecting hydrogen peroxide component.
A number of proposals have been made for delaying release of the neutralizing agent until after the disinfecting step is at least substantially complete. Some of these proposals include combining regimen steps and system components. Kruse, et al., in U.S. Pat. No. 4,767,559, form a one step cleaning/disinfecting tablet that includes a solid outer layer that is the disinfecting component and a solid core that comprises the neutralizing agent. The disinfecting agent may be any acid-reacting H.sub.2 O.sub.2 generating compound such as potassium persulfate, melamine perhydrate and is, preferably, urea peroxdhydrate. The core neutralizing agent comprises a reducing agent, such as ascorbic acid or glucose or an enzyme, such as catalase. In operation, the disinfecting agent first dissolves, followed by the core dissolving, thereby neutralizing the residual disinfecting agent. A difficulty with this product is that the process for making the outer layered/core tablet is complex which adds significant cost such that a commercial product has yet been successfully marketed using this concept.
Kaspar et al, in U.S. Pat. No. 4,568,517, describe simultaneously contacting lenses with a hydrogen peroxide solution and a neutralizing agent, preferably sodium thiosulfate or sodium sulfite, in a solid form such as a tablet. The neutralizer agent is provided with a coating which dissolves gradually to release neutralizer only after the disinfecting period has elapsed. The H.sub.2 O.sub.2 solution is transformed in situ into a buffered saline lens storage solution having a pH of 6.5-8.5 and a tonicity of 200-450 milliosmol per kg solution. A difficulty with the preferred sodium thiosulfate tablet is that it is large in size, making this approach unpractical.
A further difficulty with controlled release systems is that of providing adequate flexibility in release times and profiles, as well as good uniformity of release. Schafer et al., in U.S. Pat. No.5,011,661, describes controlled release of neutralizing agent into a peroxide system through an insoluble, yet semi-permeable membrane coating or capsule. The membrane comprises various polymers and triacetin for controlling release. Park et al., in U.S. Pat. No. 5,145,644, describes a method for coating a tablet with a controlled release water soluble polymer employing a water and ketone solvent. The ketone containing solvent is said to produce increased uniformity of coating.
A further aspect of proper contact lens care and maintenance is cleaning of the lenses of debris and contaminants that accumulate from daily wear in the eyes. As is well known, proteins, such as lysozyme, and oily substances, such as lipids, deposit on the lens during wear, eventually interfering with comfort and visual acuity. Typically, surfactants are combined to form a daily cleaner for removing the lipid contaminants. Proteolytic enzymes are employed on a weekly basis for removing protein contaminants.
Since cleaning regimens do not provide sufficient disinfecting, separate disinfecting steps always follow cleaning before the lenses are placed on the eye or in storage. In general, it is thought that the disinfecting regimens do not provide significant cleaning. Thus, forming a complete lens care regimen requires ensuring that the various cleaning regimens are compatible with a disinfecting regimen, such as the H.sub.2 O.sub.2 /neutralizer system described above and of particular interest herein.
Hydrogen peroxide disinfecting/neutralizing systems and methods remain relatively complex and require somewhat inconvenient regimens, making combination with cleaning systems difficult. Having a complete lens care disinfecting system in a single, dry package that need only be combined with a preserved saline solution would be advantageous over prior art systems for forming less complex lens care regimens. Such a system would be particularly advantageous where the disinfecting system itself provides significant cleaning efficacy and is otherwise particularly amenable to combination with conventional cleaning surfactants and protelytic enzymes in a convenient delivery package. Such a system would promote compliance with lens care regimens by providing convenient packaging and delivery systems, as well as a reduction in the number of regimen steps required and solutions involved that must be mixed and maintained.